1. Field of the Invention
The present invention relates to a self-emissive organic display device, and more particularly, to a time-divisional driving type organic electroluminescent display device in which red, green and blue light emitting elements are time-divisionally driven by one driving element and a driving method of the time-divisional driving type organic electroluminescent display device.
2. Description of Related Art
Liquid crystal display (LCD) device and organic electroluminescent display device are often used in portable information appliances due to their lightweight and thin characteristics. The organic electroluminescent display device is being noticed as the next generation flat panel display device as the organic electroluminescent display device has better luminance and viewing angle characteristics compared to the LCD device.
Ordinarily, one pixel of an active matrix organic electroluminescent display device includes red, green and blue unit pixels, wherein each red, green and blue unit pixel is equipped with an electroluminescent (EL) device. Red, green and blue organic emitting layers are respectively interposed between anode electrode and cathode electrode in each EL device so that light is emitted from the red, green and blue organic emitting layers by a voltage applied to the anode electrode and cathode electrode.
FIG. 1 illustrates structure of a conventional active matrix organic electroluminescent display device.
Referring to FIG. 1, a conventional active matrix organic electroluminescent display device 10 includes a pixel part 100, a gate line driving circuit 110, a data line driving circuit 120 and a control part (not illustrated in FIG. 1). The pixel part 100 includes a plurality of gate lines 111˜11m for providing scan signals S1˜Sm from the gate line driving circuit 110, a plurality of data lines 121˜12n for providing data signals DR1, DG1, DB1˜DRn, DGn, DBn from the data line driving circuit 120 and a plurality of power supply lines 131˜13n for providing power supply voltage VDD1˜VDDn.
The pixel part 100 includes a plurality of pixels P11˜Pmn arranged in a matrix format and connected to the plurality of gate lines 111˜11m, the plurality of data lines 121˜12n and the plurality of power supply lines 131˜13n. Each of the pixels P11˜Pmn includes three unit pixels, i.e., corresponding ones of red, green and blue unit pixels PR11˜PRmn, PG11˜PGmn, PB11˜PBmn, so that each of the red, green and blue unit pixels PR11˜PRmn, PG11˜PGmn, PB11˜PBmn is connected to a corresponding one of the gate lines, a corresponding one of the data lines and a corresponding one of the power supply lines.
For example, a pixel P11 includes a red unit pixel PR11, a green unit pixel PG11 and a blue unit pixel PB11, and is connected to a first gate line 111 for providing a first scan signal S1, a first data line 121 and a first power supply line 131.
In more detail, the red unit pixel PR11 of the pixel P11 is connected to the first gate line 111, an R data line 121R for providing an R data signal DR1 and an R power supply line 131R. In addition, the green unit pixel PG11 is connected to the first gate line 111, a G data line 121G for providing a G data signal DG1 and a G power supply line 131G. Further, the blue unit pixel PB11 is connected to the first gate line 111, a B data line 121B for providing a B data signal DB1 and a B power supply line 131B.
FIG. 2 illustrates a pixel circuit P11 of a conventional organic electroluminescent display device. In particular, FIG. 2 illustrates a circuit diagram of the pixel P11 of FIG. 1, which includes red, green and blue unit pixels.
Referring to FIG. 2, the red unit pixel PR11 of the pixel P11 includes a switching transistor M1_R for which the scan signal S1 applied from the first gate line 111 is supplied to a gate, and the data signal DR1 is supplied to a source from the red data line 121R. The red unit pixel PR1l also includes a driving transistor M2_R for which a gate is connected to a drain of the switching transistor M1_R, and a power supply voltage VDD1 is supplied to a source from the power supply line 131R. Further, the red unit pixel PR11 includes a capacitor C1_R connected between the gate and the source of the driving transistor M2_R, and a red EL device EL1_R having an anode connected to a drain of the driving transistor M2_R and a cathode connected to a ground voltage VSS.
Similarly, the green unit pixel PG11 includes a switching transistor M1_G for which the scan signal S1 applied from the first gate line 111 is supplied to a gate, and the data signal DG1 is supplied to a source from the green data line 121G. The green unit pixel PG1l also includes a driving transistor M2_G for which a gate is connected to a drain of the switching transistor M1_G, and the power supply voltage VDD1 is supplied to a source from the power supply line 131G. Further, the green unit pixel PG11 includes a capacitor C1_G connected between the gate and the source of the driving transistor M2_G, and a green EL device EL1_G having an anode connected to a drain of the driving transistor M2_G and a cathode connected to a ground voltage VSS.
Further, the blue unit pixel PB11 includes a switching transistor M1_B for which the scan signal S1 applied from the first gate line 111 is supplied to a gate, and the data signal DB1 is supplied to a source from the blue data line 121B. The blue unit pixel PB11 also includes a driving transistor M2_B for which a gate is connected to a drain of the switching transistor M1_B, and the power supply voltage VDD1 is supplied to a source from the power supply line 131B. Further, the blue unit pixel PB11 includes a capacitor C1_B connected between the gate and the source of the driving transistor M2_B, and a blue EL device EL1_B having an anode connected to a drain of the driving transistor M2_B and a cathode connected to a ground voltage VSS.
In operation of the above described pixel circuit P11, the switching transistors M1_R, M1_G, M1_B of the red, green and blue unit pixels are driven, and red, green and blue data DR1, DG1, DB1 are applied to the gates of the driving transistors M2_R, M2_G, M2_B from the red, green and blue data lines 121R, 121G, 121B, respectively, when the scan signal S1 is applied to the gate line 111.
The driving transistors M2_R, M2_G, M2_B supply to the EL devices EL1_R, EL1_G, EL1_B a driving current corresponding to the difference between the data signals DR1, DG1, DB1 applied to the gate and the power supply voltage VDD1 respectively supplied from the red, green and blue power supply lines 131R, 131G, 131B. The driving current applied through the driving transistors M2_R, M2_G, M2_B to drive the pixel P11 drives the EL devices EL1_R, EL1_G, EL1_B. The capacitors C1_R, C1_G, C1_B store the data signals DR1, DG1, DB1 applied, respectively, to the red, green and blue data lines 121R, 121G, 121B.
Operations of a conventional organic electroluminescent display device having the above described structure are described as follows in reference to driving waveform diagrams of FIG. 3.
First, the first gate line 111 is driven, and pixels P11˜P1n connected to the first gate line 111 are driven when the scan signal S1 is applied to the first gate line 111.
In other words, the switching transistors of the red, green and blue unit pixels PR11˜PR1n, PG11˜PG1n, PB11˜PB1n of the pixels P11˜P1n connected to the first gate line 111 are driven by the scan signal S1 applied to the first gate line 111. Red, green and blue data signals D(S1) (DR1˜DRn, DG1˜DGn, DB1˜DBn) are simultaneously applied to the gates of the driving transistors of the red, green and blue unit pixels, respectively, through the red, green and blue data lines 121R˜12nR, 121G˜12nG, 121B˜12nB composing first to nth data lines 121˜112n according to the driving of the switching transistors.
The driving transistors of the red, green and blue unit pixels supply a driving current corresponding to the red, green and blue data signals D(S1) (DR1˜DRn, DG1˜DGn, DB1˜DBn) applied to the red, green and blue data lines 121R˜12nR, 121G˜12nG, 121B˜12nB, respectively, to the red, green and blue EL devices. Therefore, the EL devices of the red, green and blue unit pixels PR11˜PR1n, PG11˜PG1n, PB11˜PB1n of the pixels P11˜P1n connected to the first gate line 111 are simultaneously driven when the scan signal S1 is applied to the first gate line 111.
Similarly, if a scan signal S2 for driving a second gate line 112 is applied, data signals D(S2)(DR1 DRn, DG1 DGn, DB1 DBn) are applied to red, green and blue unit pixels PR21˜PR2n, PG21˜PG2n, PB21˜PB2n of pixels P21˜P2n connected to the second gate line 112 through red, green and blue data lines 121R˜12nR, 121G˜12nG, 121B˜12nB composing first to nth data lines 121˜12n. 
EL devices of the red, green and blue unit pixels PR21˜PR2n, PG21˜PG2n, PB21˜PB2n of the pixels P21˜P2n connected to the second gate line 112 are simultaneously driven by a driving current corresponding to the data signals D(S2)(DR1˜DRn, DG1˜DGn, DB1˜DBn).
EL devices of red, green and blue unit pixels PRm1˜PRmn, PGm1˜PGmn, PBm1˜PBmn of pixels Pm1˜Pmn connected to the mth gate line 11m are simultaneously driven according to red, green and blue data signals D(Sm)(DR1˜DRn, DG1˜DGn, DB1˜DBn) applied to the red, green and blue data lines 121R˜12nR, 121G˜12nG, 121B˜12nB when a scan signal Sm is finally applied to mth gate line 11m by repeating the foregoing actions.
Therefore, an image is displayed by sequentially driving pixels (P11˜P1n)˜(Pm1˜Pmn) connected to the respective gate lines 111˜11m, thereby driving pixels during one frame when the scan signals S1˜Sm are sequentially applied starting with the first gate line 111 and ending with the mth gate line 11m. 
However, in an organic electroluminescent display device having this structure, each pixel includes red, green and blue unit pixels, and driving elements for driving red, green and blue EL devices (i.e., a switching thin film transistor, a driving thin film transistor and a capacitor) are respectively arranged per the red, green and blue unit pixels. Further, data lines and power supply lines for supplying data signal and power supply ELVDD to each driving element are respectively arranged per the unit pixels.
Therefore, three data lines and three power supply lines are arranged per pixel, and at least six transistors including three switching thin film transistors and three driving thin film transistors and at least three capacitors are required in each pixel. On the other hand, at least four signal lines are required per red, green and blue unit pixels as a separate emission control line for providing emission control signal is required in case that each pixel is controlled by emission control signals. Therefore, the circuit structure for the pixels in a conventional organic electroluminescent display device is complicated as a plurality of wirings and a plurality of elements are arranged per each pixel, and yield is reduced as probability of generating defects is increased accordingly.
Further, the area of each pixel is reduced as the resolution of the display device is being increased, and not only is it difficult to arrange many elements on one pixel, but also the aperture ratio is reduced accordingly.